The disclosed embodiments of the present invention relate to a camera auto-focus technique, and more particularly, to a camera auto-focus apparatus for performing a lens position compensation to determine a focused lens position and a related camera auto-focus method.
Recently, camera systems are widely used in a variety of applications such as mobile phones and tablets. The mobile phone market is continuing to increase explosively, especially with integration of high-end camera functions. Conventional camera phones have used manual focusing techniques in which users would adjust the location of lens with their own hands for producing a focused image. However, user's skill will limit the image quality since it is hard to focus on the target object precisely. Therefore, phone manufacturers are developing camera phones with auto-focus (AF) function to enhance the image quality. The AF function can solve above-mentioned problems and provide users with high quality images as well as ease of using the camera phones.
Nowadays, phone manufacturers require a camera auto-focus apparatus with a more compact volume and a lower production cost. Accordingly, a VCM (Voice Coil Motor) type lens module is commonly used. With regard to the VCM type lens module, it includes a lens and a VCM actuator, where the VCM actuator is used to control a position of the lens through pushing/pulling a spring mechanism. In general, the focus value is biased at a moving frame that is captured when the lens is still moving due to damping of the spring mechanism. Further, the spring mechanism has different damping responses for opposite lens scan directions, including a lens scan direction from an infinite side to a macro side and a lens scan direction from a macro side to an infinite side. Hence, a focused lens position found in one lens scan direction does not coincide with a focused lens position found in the other lens scan direction, which results in auto-focus inconsistency. The auto-focus inconsistency issue caused by damping of the spring mechanism can be avoided when the focus values are obtained after the lens become stable. However, such an auto-focus design will result in degradation of the auto-focus speed.
Thus, there is a need for an innovative camera auto-focus design which is capable of solving the auto-focus inconsistency issue without degradation of the auto-focus speed.